Electric discharge lamp



June 10, 1941 L. BURNS Re. 21,823

ELECTRIC DISCHARGE LAMP Original Filed Dec. 20, 1954 INVENTOR ATTORNEY Reissuetl June 10, 1941 UNITED STATES PATENT OFFICE 21,823 I ELECTRIC DISCHARGE LAMP Laurence Burns, Swampscott, Masa, assignor to Hygrade Sylvania Corporation, Salem, Mass., at corporation 01' Massachusetts Original No. 2,061,892, dated Nomi... 24, 1936,

Serial No. 758,406, December 20, 1034. Application ior reissue November 23, 1938, Serial No.

4 Claims.

This invention relates to electric lamps and more particularly to the lamps of the gas or vapor discharge type.

An object of the invention is to improve the I efllciency of discharge lamps of the vapor arc type, although certain features of the invention are advantageously applicable to other types of discharge lamps.

In a vapor arc discharge lamp, particularly where the vapor is at relatively high pressure when the lamp is in operation, the eiilciency oi thelamp is a function of the vapor pressure and the power input required to maintain such vapor pressure. It has been found that in a high pressure vapor arc lamp employing mercury as the vaporizable agent, a considerable part of the radiation from the arc is hr the infra-red region. Since the rays in the infra-red region have negligible optical efl'ect, ordinarily the passage-of these rays through the enclosing envelope represents a corresponding loss in luminous eiliciency. In accordance with the present invention it is proposed to so design the enclosing envelope that these otherwise useless infrared radiations are utilized to conserve the heat of, the arc, and thus not only reduce the interval required for "lighting up" and cooling of the lamp, but also serve to increase the efllciency of the lamp when in operation.

Accordingly one of the principal objects of this invention is to provide a mercury arc lamp with an enclosing envelope which substantially absorbs and conserves the infra-red radiations.

Another feature of the invention relates to a mercury vapor arc lamp wherein the enclosing envelope is designed to absorb and conserve a substantially large percent of the ultra-violet radiation.

A feature of the invention resides in the provision of a high pressure mercury vapor arc lamp having an envelope designed to have its maximum wave transmission in the hand between the ultraviolet and infra-red ranges of wave length.

Another feature of the invention relates to a high pressure mercury vapor arc lamp with an enclosing envelope of boro-silicate glass having incorporated therein a small percent oit ferrous oxide or similar metallic oxide to increase the heat conservation of the lamp.

Other features and advantages of the invention not specifically enumerated will be apparent after a consideration of the following detailed descriptionand the appended claims.

While the invention ,will be disclosed herein as embodied in one particular lamp structure, it

will be understood that this is done merely for Pu poses o1 explanation and not by way of limitation.

In the drawing, there is shown in partial sec tion, a view of a lamp embodying features of the invention. The numeral I represents an inher enclosing envelope preferably of a hard glass, and having mounted at opposite ends thereof -af pair of refractory electrodes 2, 3. These electrodes are provided with respective lead-in wires 4, 5, and interposed between the envelope and the lead-in wires are graded seals, each comprising a shallow cup-like cap member 6 of relatively soft glass into which is sealed the lead-in wire, the latter having thereon a suitable glass bead of hero-silicate or similarglass such for example as "Nonex" glass. Preferably, although not necessarily, the caps 6 are buttsealed to ,the respective ends of the envelope proper as indicated! by the numerals I, Preferably also, each electrode is so mounted that the major portion of its length is in advance of the associated seal and is also so positioned that during operation of the lamp there is sumcient heat in the electrode chamber including the cap to prevent condensation of mercury therein. While electrodes 2, 3, may be of any well-known structure they are preferably, although not necessarily, of tungsten wire doubly coiled as described in detail in application Serial No. 752,016, filed- November 8, 1934.

The sealed envelope I is previously provided with the proper filling of mercury so that when the lamp is operating at its rated! wattage, all the mercury is maintained in vapor form and at relatively high pressure, for example in the range between mins. and 3000 mms. oi mercury. The envelope I is supported in any suitable manner within another evacuated envelope II which is provided with a re-entrant press II through which pass the conductors connecting to the lead wires 4 and I. The envelope I may be provided with an ordinaryMogul type base I! so that the lamp may be used in conventional lamp sockets. For a further detailed description of the structure of lamp shown in the drawing, reference may be had to application Serial No. 758,405, flied December 20, 1934.

In accordance with the present invention either the inner envelope I or the outer envelope III or both have their main body portions of a specially chosen glass which is capable of absorbing to a marked extent radiations in the infra-red and ultra-violet wave length ranges. Thus the envelope I may be of an ordinary borosiiicate glass ium, magnesium, calcium, zinc, strontium, cadmium. barium may be employed so long as the percentage of these elements is relatively small and does not materially affect the ton characteristics of the glass in the desired range of wave lengths. For example it has been fotmd that in the type of lamp disclosed the green and yellow spectral lines at about 546 and 579 millimicrons wave length are the ones that chiefly aiiect the eye in producing luminosity. It has also been found that the incorporation of the small percentage of oxides above mentioned in the glass envelope increases the absorption of the infra-red and blue and ultra-violet rays to a very marked extent without correspondingly reducing the transmission characteristics of the envelope for the desired range of wave lengths namely those in the green and yellow parts of the spectrum. It has also been found that by incorporating a relatively small percentage of tin in the glass that the desired characteristics are improved.

When the outer envelope II has incorporated therein materials as above set forth, this outer envelope absorbs the infra-red, blue and ultraviolet radiations not only from the arc itself but also the corresponding radiations from the envelope I which during operation is at a relatively high temperature. Accordingly if desired, the envelope I may be made of any hard glass such as Pyrex" or combustion tubing as set forth in application Serial No. 758,405, filed December 20, 1934, and the outer envelope Ill may alone be designed to achieve the desired conservation of the heating radiations. n the other hand the envelope ll may be made of ordinary lead glass while the envelope I may be designed to achieve the desired conservation of heat as above set forth. Instead of incorporating the materials in the body of the glass envelope to achieve the selective absorptionand transmission characteristic, a similar result may be obtained by providing these envelopes with suitable coatings of sufficient thinness to transmit the desired radiations chiefly in the yellow .and green ranges while materially absorbing and conserving the radiations in all other ranges. As examples of such coatings may be mentioned the following: boron oxide with a small percent of ferrous oxide, or boron silicate with a small percent of ferrous oxide.

Various changes and modifications may be made herein without departing from the spirit and scope of the invention.

What I claim is:

i. A vapor discharge lamp comprising a pair of spaced electrodes immersed in a vapor adapted to sustain an arc-like discharge therebetween, having the greatest visual effect in the green and yellow radiations. and means for conserving the heat of the are including an enclosing envelope of 'borosilicate glass having incorporated therein a small percentage of ferrous oxide and tin to increase the absorption of the infra-red and ultraviolet radiations while allowing the yellow and green radiations to pass.

2. A lamp of the type described comprising an inner envelope containing a mercury vapor filling, a pair of spaced electrodes mounted within said envelope, an outer envelope enclosing the first envelope, one of said envelopes having incorporated therein a small percentage of ferrous oxide and tin to increase the absorption of infra-red and ultraviolet radiations without correspondingly affecting the yellow and green radiations.

3. A vapor discharge lamp comprising a pair of spaced electrodes immersed in a vapor adapted to sustain an arc-like discharge therebetween, having the greatest visual eflect in the green and yellow radiations, and means for conserving the heat of the are including an enclosing envelope of borosilicate glass having incorporated therein a small percentage of tin and one at least of the following oxides: iron, zinc, beryllium, to increase the absorption of the infra-red and ultra-violet radiations while allowing the yellow and green radiations to pass.

4. A vapor discharge lamp comprising a pair of spaced electrodes immersed in a vapor adapted to sustainan arc-like discharge therebetween, having the greatest visual effect in the green and yellow radiations, and an outer envelope encloslng an inner silicate envelope having incorporated therein a small percentage of tin and at least one of the following oxides: iron, zinc, beryllium, to increase the absorption of at least the ultraviolet radiation while allowing the yeliow and green radiations to pass.

LAURENCE BURNS. 

